1. Field of the Invention
The present invention relates to an appearance inspection method and appearance inspection apparatus for performing appearance inspection for uneven exposure, de-focusing, poor coating, scratches, and the like of an inspection object, by irradiating illumination light on objects to be inspected such as substrates which are used in the production of micro devices such as semiconductor elements, imaging elements (CCDs, etc.) liquid crystal displays and thin film magnetic heads.
2. Description of the Related Art
Recently with the advance in high integration of semiconductor devices, in the fields of inspection and measurement, the resolution which is required with respect to inspection devices for observing and inspecting for defects in patterns on wafers and reticules has followed continual refinements with each successive generation.
Despite the low level of demand for improvements in resolution for inspection in the area of appearance inspection for inspecting for uneven coating, uneven exposure, de-focusing, poor coating, scratches and the like of resist on a wafer, the importance which is being placed on reducing production costs has resulted in expectations for realizing an automated inspection device for automatically carrying out the aforementioned appearance inspections which have heretofore relied upon visual inspection.
In the past, for this kind of appearance inspection apparatus, a method is adopted where the entire wafer surface being the object to be inspected, on an inspection stage, is illuminated with a uniform light source, and the entire wafer surface is photographed at one time using a two-dimensional camera and taken as an inspection image. Furthermore, Japanese Patent Application, First Publication No. 8-75661, discloses a method for inspecting for defects such as scratches, impurities and stains on substrates, by receiving diffracted light from repeated patterns on the substrate.
Since when a substrate is inspected according to this method, the same level of throughput is required as with a conventional inspection carried out visually by a trained inspector, it is necessary for example, to make the amount of time taken to photograph an image of the substrate the same as that taken in a visual inspection. Hence, the method of photographing the entire substrate at the same time has recently been adopted in an attempt to increase throughput.
However, the following type of problems are to be found with regard to the aforementioned conventional appearance inspection methods and appearance inspection apparatuses.
The detection of the above-mentioned defects differs greatly according to the type of fault. For instance, in the inspection for impurities and scratches on the surface of the object to be inspected, through the use of light illumination, scattered light emanating from a defect on the surface being inspected is utilized. Additionally, in the inspection for uneven coating, uneven exposure, de-focusing and poor coating on the resist, the diffracted light which is generated from the object to be inspected by light illumination is used.
What is more, the main objective of automating an inspection which has until now relied upon visual inspection, necessitates the implementation of an inspection which follows the inspection procedure which has heretofore been carried out by an inspector. Accordingly, it is necessary to follow in order the several inspection steps which, with conventional appearance inspection methods and appearance inspection apparatuses, entail such things as separately photographing the substrates in accordance with the aforementioned various inspection procedures. Hence there is the disadvantage that inspection throughput time is increased.
The present invention takes into consideration the above points with the object of providing an appearance inspection method and an appearance inspection apparatus which has the ability to shorten the inspection throughput time, even when carrying out automatically the same inspection as that carried out visually.
In order to achieve the above objective, an appearance inspection method according to the present invention is characterized in comprising: a first step for inspecting an object to be inspected by illuminating the object to be inspected mounted on a first stage and receiving scattered light therefrom, a second step for inspecting the object to be inspected by illuminating the object to be inspected mounted on a second stage and receiving diffracted light therefrom, and a transfer step for transferring the object to be inspected between the first stage and the second stage so that either one of the first step and the second step is carried out after the other.
Accordingly, with the appearance inspection method of the present invention, in the case where the object to be inspected is a substrate which has been coated with resist, then while inspecting in the first step for scratches and impurities on the surface of the object to be inspected using the scattered light generated from the object to be inspected on the first stage, it is possible to inspect concurrently in the second step for uneven coating, uneven exposure, de-focusing and poor coating on the resist using the diffracted light generated from the object to be inspected on the second stage. Furthermore, when either one of the first step or the second step is completed, then in the transfer step the object to be inspected is transferred between the first stage and the second stage. After this, the inspection of the other step is carried out on the transferred object to be inspected.
As a result, with this appearance inspection method, the effect is obtained that it is possible to prevent a lengthening in the throughput time even when a plurality of inspections are automatically carried out, while maintaining the same functions as for the conventional inspection which is carried out visually.
With an appearance inspection method of an embodiment of the present invention, in accordance with the transfer by the transfer step of the object to be inspected from one stage of either the first stage and the second stage, a new object to be inspected is transferred to the one stage.
According to this appearance inspection method, it is possible to simultaneously execute the first step and the second step concurrently, enabling a substantial improvement in the inspection throughput.
With an appearance inspection method of another embodiment of the present invention, prior to inspection of the object to be inspected, an alignment step is carried out for aligning the object to be inspected at a predetermined location by moving a stage.
According to this appearance inspection method, it is possible to perform inspection at the optimum position corresponding to the object to be inspected, and thereby improve inspection accuracy. Furthermore, the inspection not only makes it possible to detect the presence of defects, but also enables the coordinate position where the defects occurs to be specified. Therefore, it is easy to undertake a subsequent so-called micro inspection for making a concentrated inspection of the region.
With an appearance inspection method of another embodiment of the present invention, after completion of one step of the first and second steps, the object to be inspected is pre-aligned to a direction required for the other step, while remaining mounted on the stage used for the one step, after which the object to be inspected is transferred to the stage of the other step by the transfer step.
According to this appearance inspection method, inspection at the optimum position corresponding to the object to be inspected is also possible in the other step, enabling an improvement in inspection accuracy. Furthermore, as with the first inspection, it is possible to specify the coordinate position where the defect occurs, and hence post inspection micro inspection can be easily performed. In addition, since it is no longer necessary to provide a separate mechanism for alignment for the stage which is used in the second step, it is possible to also realize device miniaturization and a reduction in costs.
With an appearance inspection method of another embodiment of the present invention, a plurality of long inspection time steps are carried out concurrent with a short step, and transfer is carried out so that the object to be inspected which has just completed the long step is transferred to the short step by turns.
According to this appearance inspection method, it is possible to set the period for performing the short inspection time step on the short inspection time side without needing to match this with the period for performing the long inspection time step, thereby enabling a further reduction in throughput time.
With an appearance inspection method of another embodiment of the present invention, based on the inspection results for the object to be inspected in one step, an inspection mode for the other step is changed.
According to this appearance inspection method, since it is possible in the other step to set an additional inspection in addition to the usual inspection, and to perform a concentrated inspection of parts where defects are likely, it is possible to reliably detect even smaller defects, thereby enabling an improvement in inspection accuracy.
With an appearance inspection method of another embodiment of the present invention, based on the inspection results for the object to be inspected in one step, a decision is made to either execute or cancel the other step.
According to this appearance inspection method, it becomes possible to cancel a redundant step where inspection is performed in the other step with respect to an object to be inspected which is not suitable for use, thus enabling an improvement in throughput.
With an appearance inspection method of another embodiment of the present invention, in the case where the other step is cancelled based on the inspection results for the object to be inspected in the one step, the object to be inspected is transferred by way of the stage used in the other step.
According to this appearance inspection method, inspection can be performed as prescribed without interrupting the sequence of the transfer of the object to be inspected.
As for the appearance inspection apparatus of the present invention, this comprises: a first stage for inspecting an object to be inspected by illuminating the object to be inspected and receiving scattered light therefrom, a second stage for inspecting the object to be inspected by illuminating the object to be inspected and receiving diffracted light therefrom, and a transfer mechanism for transferring the object to be inspected between the first stage and the second stage so that either one of the inspection of the first stage and the inspection of the second stage is carried out after the other.
According to the appearance inspection apparatus of the present invention, while inspecting for scratches and impurities on the surface of the object to be inspected using the scattered light generated from the object to be inspected on the first stage, it is possible to inspect concurrently for uneven coating, uneven exposure, de-focusing and poor coating on the resist using the diffracted light generated from the object to be inspected on the second stage. Furthermore, when either one of the inspections of the inspections on the two stages is completed, the transfer mechanism transfers the object to be inspected between the first stage and the second stage. The inspection on the other stage is then carried out on the transferred object to be inspected. As a result, it is possible to prevent a lengthening in the throughput time even when a plurality of inspections are automatically carried out, while maintaining the same functions as for the conventional inspection which is carried out visually.
With an appearance inspection apparatus of another embodiment of the present invention, the alignment mechanism is constructed so as to perform alignment of the object to be inspected by moving the first stage or the second stage.
According to this appearance inspection apparatus, it is possible to perform inspection at the optimum position corresponding to the object to be inspected, and thereby improve inspection accuracy. Furthermore, the inspection not only makes it possible to detect the presence of defects, but also enables the coordinate position where the defects occurs to be specified. Therefore, it is easy to undertake a subsequent so-called micro inspection for making a concentrated inspection of the region.
With an appearance inspection apparatus of a further embodiment of the present invention, the construction is such that the illumination light used for the first stage and the illumination light used for the second stage share a single light source.
According to this appearance inspection apparatus, since the number of light sources is reduced, it possible to realize device miniaturization and a reduction in costs.